Duct for a toilet bowl ventilation system



FIG. 1 is a perspective view of a duct for a toilet bowl ventilation system showing my new design from the top, one end, and one side; and,

FIG. 2 is a perspective view thereof showing my new design from the bottom, and end and side opposite that shown in FIG. 1. 

The ornamental design for a duct for a toilet bowl ventilation system, as shown and described. 